1. Field of the Invention
The present invention relates to an electric vehicle and, more particularly, to a battery charger mounted on board the vehicle. While the invention is subject to a wide range of applications, it is especially suited for use in electric vehicles that utilize batteries or a combination of batteries and other sources, e.g., a heat engine coupled to an alternator, as a source of power, and will be particularly described in that connection.
2. Discussion of the Related Art
The internal combustion automobile has long supplied an important share of the world's transportation needs. However, it is inevitable that petroleum reserves which supply fuel for the global internal combustion vehicle fleet will sooner or later decline to a point where the cost of fuel for internal combustion vehicles becomes unacceptable. Another factor clouding the future of internal combustion vehicles is the ever more stringent regulation of exhaust emissions from such vehicles. These and other factors have led to increasing efforts to develop a commercially viable alternative to the internal combustion vehicle which uses an electric propulsion system.
For an electric vehicle to be commercially viable, its costs and performance should be competitive with that of its internal combustion counterparts. Typically, the vehicle's propulsion system and battery are the main factors which contribute to the vehicle's cost and performance competitiveness. In particular, consumers may be reluctant to give up their internal combustion automobile for an electric vehicle because of concern that an electric vehicle will not have sufficient range to return to a station for charging of its battery. The uncertainties caused by a lack of a precise way to measure the remaining charge in the batteries and the significant range reduction suffered by batteries in cold weather climates justifies this concern. In addition, most consumers desire the capability to charge their batteries at home overnight. Therefore, an on-board battery charger that can be plugged into a standard residential 230-volt receptacle is an important factor in the acceptance and use of electric vehicles.
As yet, there is no standard for batteries used to power electric vehicles. Some of the more common types include conventional lead-acid batteries, high density lead-acid batteries, deep-discharge lead-acid batteries, nickel-cadmium batteries, nickel-metal batteries, and nickel-metal hydride batteries. Newer and more advanced battery types are currently under development. It is possible that after an electric vehicle is sold, a newer and better performing electric battery may become readily available, creating an incentive to install a new battery in the vehicle.
Even for an individual battery, the terminal voltage varies widely according to its state of charge. Thus, expected terminal voltage of an electric vehicle battery can range from around 100 volts up to and above 600 volts. It is not economically feasible to design a separate battery charger for each specific type of battery or battery pack voltage. Neither is it economically sound to require replacement of a battery charger when the battery type is upgraded or otherwise changed. Therefore, there is a requirement for a universal on-board battery charger capable of supplying charging current over a wide range of terminal voltages.
Another requirement for an on-board battery charger is that it be small and lightweight, since each pound of extra weight carried by the vehicle represents a shorter distance that can be travelled before "refueling" (recharging). The battery charger must also be self-contained because 12-volt power, pumps, or cooling fluids or other auxiliary support capabilities will not always be available. Therefore, the battery charger must be air cooled and must supply its own operating power from the 230-volt charging source. Since the battery charger is located on-board the vehicle, it must exist in an automotive environment and be capable of operation from -40.degree. C. to +85.degree. C. Moreover, since the charger will be plugged into electrical outlets where lethal voltages are present, it must pose no safety hazard during operation. The only way to ensure safe operation is to provide the capability for the battery charger to operate through a standard ground fault circuit interrupter (GFCI) as is commonly employed in residential environments to monitor and protect from fault current. None of the existing electric vehicle battery chargers currently meets all of the requirements set forth above.